The invention relates to a supercharged internal combustion engine with exhaust gas recirculation and a first group of cylinders and a second group of cylinders which operates in accordance with the spender cylinder principle wherein specifically exhaust gas from the second group of cylinders is recirculated. The engine includes an exhaust gas collection duct having a first section connected to the first group of cylinders and a second section connected to the second group of cylinders for receiving exhaust gas therefrom and conducting it to the turbine or, respectively, via an exhaust gas recirculation line, to a charge air line supplying fresh gas to the cylinders.
An internal combustion engine with these features is disclosed in U.S. Pat. No. 4,249,382. In a first embodiment, an internal combustion engine with six cylinders and an exhaust gas turbocharger is shown wherein one cylinder is used as a recirculation exhaust gas supply cylinder (spender cylinder). The exhaust gas of the other cylinders is combined in a first section of the exhaust gas collection line and is supplied via an exhaust gas collection line to the turbine of the exhaust gas turbocharger. The exhaust gas of the recirculation exhaust gas supply cylinder is collected in a second section of the exhaust duct and is returned, via an exhaust gas recirculation cooler to the charge air intake duct. With this arrangement, a constant exhaust gas recirculation rate of 16% is provided.
In the arrangement described in following description more than one cylinder can be used for returning exhaust gas to the intake duct or directing it, selectively to the turbine.
In a second embodiment of the state of the art referred to above, the first and the second groups of cylinders comprise each the same number of cylinders. Additionally, at the point of connection to the exhaust recirculation line there is a branch off line leading to the first exhaust gas line. The branch-off line includes an electrical control device by which the exhaust gas flow from the exhaust gas recirculation line to the first exhaust gas line can be controlled.
With this design, a maximum exhaust gas recirculation rate of 50% is obtainable. Because of the higher exhaust gas back pressure in the exhaust gas recirculation line an exhaust gas recirculation supply cylinder has to perform a greater exhaust gas discharge work which results in a higher fuel consumption and a higher thermal load. This applies particularly to high-pressure exhaust gas recirculation as it is required for supercharged engines. With exhaust gas recirculation rates of for example 20% in this arrangement, 50% of the cylinders are operated with an increased exhaust gas back pressure which has a detrimental effect on the fuel consumption. In practice, it is attempted to find a compromise between, on one hand, the necessary exhaust gas recirculation rate and consequently, the number of cylinders in the second group of cylinders and, on the other hand, the fuel consumption. A further disadvantage of the second embodiment described above resides in the fact that an exhaust gas recirculation rate of 0% cannot be established over the whole operating range, for example, when the pressure level in the charge air supply line is lower than the pressure level in the second exhaust gas line.
It is the object of the present invention to provide a supercharged internal combustion engine with exhaust gas recirculation, which includes a first cylinder group and a second cylinder group for which an exhaust gas recirculation rate of 0% can be set over a large operating range and the second cylinder group always includes only a minimum number of cylinders.